Preparation of a high-concentration Au nanoring (NR) water solution and its applications to the enhancement of image contrast in optical coherence tomography (OCT) and the generation of the photothermal effect in a bio-sample through localized surface plasmon (LSP) resonance are demonstrated. Au NRs are first fabricated on a sapphire substrate with colloidal lithography and secondary sputtering of Au, and then transferred into a water solution through a liftoff process. By controlling the NR geometry, the LSP dipole resonance wavelength in tissue can cover a spectral range of 1300 nm for OCT scanning of deep tissue penetration. The extinction cross sections of the fabricated Au NRs in water are estimated to give levels of 10(-10)-10(-9) cm(2) near their LSP resonance wavelengths. The fabricated Au NRs are then delivered into pig adipose samples for OCT scanning. It is observed that, when resonant Au NRs are delivered into such a sample, LSP resonance-induced Au NR absorption results in a photothermal effect, making the opaque pig adipose cells transparent. Also, the delivered Au NRs in the intercellular substance enhance the image contrast of OCT scanning through LSP resonance-enhanced scattering. By continuously OCT scanning a sample, both photothermal and image contrast enhancement effects are observed. However, by continually scanning a sample with a low scan frequency, only the image contrast enhancement effect is observed.
We propose and describe a micro-machined tunable metamaterial terahertz filter based on graphene. The device structure consists of periodic metallic rings with several gaps where tunable graphene stripes are located. We demonstrate that the filter resonance frequency can be adjusted easily by varying the conductivity of graphene and implement this by changing the number of stacked graphene layers. Moreover, the proposed design is scalable, in the sense that the resonance frequency tuning can be controlled by scaling the inner and outer radius of the metal rings. Using numerical simulations and terahertz time-domain spectroscopy measurements of the fabricated samples, we show that the resonance frequency of the structure can be altered by 40% (i.e., from ∼0.2 THz to ∼0.12 THz) by simply tuning the conductivity of graphene. Importantly, the active area of the device is ≪0.1% of the total unit cell area, which can boost the device speed upon electrostatic actuation.
Blending high content of polyhydroxyalkanoates (PHAs ≥ 30 wt.%) with polylactide (PLA) provides an effective strategy to significantly improve heat resistance of PLA fibers. However, it has proven challenging to maintain good spinnability of the PLA/PHAs blends with the high content of PHAs. In this study, a series of poly(L‐lactide) (PLLA)/poly[(R)‐3‐hydroxybutyrate‐co‐4‐hydroxybutyrate] (P34HB) blend fibers with low P34HB content (≤ 8 wt.%) is successfully fabricated with excellent spinnability. The incorporation of P34HB contributes to a substantially improved heat resistance of the PLLA/P34HB blend fibers, as evidenced by a notable reduction in boiling water shrinkage from ca. 80% to 9%. This exceptionally improved heat resistance is closely related to substantial increase in crystallinity of PLLA in the blend fibers. Specifically, the addition of low P34HB content remarkably enhances chain mobility of PLLA chains, as such reduces crystallization half‐times (t1/2) and accelerates crystallization of PLLA. In fact, the amorphous P34HB phase favors crystal growth of PLLA phase rather than heterogeneous nucleation inferred previously. These results provide a facile and effective method to produce PLLA/P34HB blend fibers with enhanced heat resistance and sound spinnability.
A battery thermal management system (BTMS) plays a significant role in the thermal safety of a power lithium-ion battery. Research on phase change materials (PCMs) for a BTMS has drawn wide attention and has become the forefront of this scientific field. Several evident limitations exist in pure PCMs, such as poor thermal conductivity and low structural stability, while porous materials could reinforce PCMs for their superior thermal performance and robustness. Most related existing reviews focused on the thermal performances of a lithium-ion BTMS by different cooling methods. However, the thermal properties of porous materials and those based composite phase change materials (CPCMs) have not been summarized, which have much influence on the thermal management effect of battery modules. Thus, research on porous-material-based CPCMs used for a lithium-ion BTMS were reviewed in this paper. The kinds of PCMs and porous materials commonly used in a lithium-ion BTMS were introduced, and the thermophysical properties and robustness of porous-material-based CPCMs were systematically analyzed. Furthermore, the thermal management effects of a porous-materialbased CPCM on a lithium-ion battery were summarized. We discussed the enhancement effects on PCMs and the advantages and limitations of various porous materials commonly used in a lithium-ion BTMS. Finally, on the basis of the current research, this paper concluded the requirement of porous material for a CPCM in a lithium-ion BTMS and the expected future research directions of porous material, including looking for a potential porous carrier, intensifying heat transfer, and enhancing anti-vibration performance.
This work studies the terahertz light propagation through graphene-based reconfigurable metasurfaces where the unit cell dimensions are much smaller than the terahertz wavelength. The proposed devices, which poses deep-subwavelength unit cell and active region dimensions can operate as amplitude and/or phase modulators in certain specific frequency bands determined by the device geometry. Reconfigurability is attained via electrostatically tuning the optical conductivity of patterned graphene layers, which are strategically located in each unit cell. The ultra-small unit cell dimensions can be advantageous for beam shaping applications.
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